Camping On an Iceberg

The world’s largest iceberg is now drifting freely in the Weddell Sea off Antarctica’s coast and into the South Atlantic. It’s about the size of Oahu, as the modded image shows. Designated A23A, it measures 46 by 37 miles and is 1,300 feet thick. It’s estimated that A23A contains more than a trillion tons of frozen water.

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First,we need to take a brief excursion into the iceberg naming system. For Antarctic icebergs, like A23A, the first letter is derived from the Antarctic quadrant in which they were originally formed or sighted. The quadrants are divided by the cardinal compass directions:

A = 0-90W (Bellingshausen/Weddell Sea)
B = 90W-180 (Amundsen/Eastern Ross Sea)
C = 180-90E (Western Ross/Wilkesland Sea)
D = 90E-0 (Amery/Eastern Weddell Sea)

The number “23” is a sequential number indicating it’s the 23rd iceberg tracked from that quadrant origin. The final “A” indicates the iceberg has calved off from a larger iceberg, and was the first to do so. Designations are assigned by the US National Ice Center (USNIC).

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A23A is what’s known as a tabular iceberg, with steep sides and a flat top like a plateau. Non-tabular icebergs include irregular shapes such as domes, spires, and asymmetric blocks. Wind, water, and sunlight can sculpt smaller icebergs into exotic shapes that evolve from the original fractured surface. Tabular icebergs will erode more uniformly, getting thinner as warmer ocean water melts it from below, and sunlight melts the upper surface (where melt pools often form). Eventually A23 will spawn A23B and continue until breakup is complete.

When A23A first broke off from the glacier back in 1986 it was still grounded on the sea floor and unable to move. Over the years it was nudged by tides, currents, and winds, and in 2020 finally broke free. It’s now drifting northward, and could run aground again on either the South Georgia or Falkland Islands. Of course, USNIC tracks these large icebergs as they present a significant hazard to maritime operations. Depending on water temperatures, A23A could persist for 3-6 years.

If you’re interested in learning more about A23A see this NPR report.

When I read that report I was intrigued by the comments from Ted Scambos, a senior research scientist at the University of Colorado in Boulder. Scambos has camped on large icebergs and recounts that “you can’t really tell you’re moving” because the motion is so slow (1-2 mph). However, winds and currents also cause the iceberg to slowly rotate, so when when you observe the sky over a period of time, the Sun, Moon and stars seem out of place. He also notes that on an iceberg as large as A23A, you could not tell by vision alone that you were on an iceberg surrounded by ocean. The edge of the iceberg would be well beyond your horizon.

His comments prompted me to speculate on other aspects of “camping on a large iceberg.” The following graphic shows A23A to scale, with a hypothetical campsite (NTS) pitched at the center of the iceberg:

For a 6 ft observer, the visual horizon on Earth’s curved surface is 4.8 km distant. On A23A it would look like winter on the Great Plains. You could hike for miles and see nothing but snow on “flat ground.” Note that I’ve curved the ice sheet to conform to the Earth’s curvature (exaggerated). It might be surprising to realize that ice can bend without breaking, but over long distances it will flex elastically like many other solids. Over the 23 mile length of A23A, measured from the center out, the amount of bending is only 15.3 ft — a deflection of 0.013%.

Further enhancing the Great Plains illusion is the stability of such a large mass of ice. You wouldn’t feel it rocking like a rowboat in response to the waves. With waves crashing into its 75 mile perimeter shoreline from all directions, their effects tend to cancel out. Even if there’s a significant imbalance due to a storm, the rotational inertia of a trillion tons of ice still wins out. A23A might slowly tilt but it would be hard to notice at the camp. The pendulum clock in your tent would run just fine.

Finally, adding to the illusion, you wouldn’t hear the sounds of ocean surf from the center of A23A. In addition to the visual horizon there’s an acoustic horizon. It’s less well defined, because how far away you can hear something depends on many variables. People who live near the ocean report hearing the surf at distances up to 12.2 km from the beach under ideal conditions, so that’s what I used for the acoustic horizon.

I doubt any of my readers will ever camp on an iceberg, so it’s not like I provided any practical information in this post. Consider it more a scientifically annotated travelogue to a place none of us are likely to visit. Planetary scientists do this all the time. Their insights enable a virtual experience of uncharted territory.

Next Week in Sky Lights ⇒ How Fast Earth Spins

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